Degreasing



Nov. 5, 1940. M. Y. SEATON nmmmsme Filed July 20, 1938 Patented Nov. 5,1940 DEGREASING Max Y. Seaton, Greenwicln'fionnu assignor to WestvacoChlorine Products Corporation, New York, N. Y., a corporation ofDelaware Application July 20, 1938, Serial No; 220,378

This invention or discovery relates to degreasing; and it comprises amethod of vapor-phase degreasing, wherein a lake or body of organicsolvent vapor is established and maintained between a supply of boilingsolvent and a supernatant atmospheric layer, and metal parts or otherobjects to be degreased are contacted with said solvent vapor body, andwherein parts of said solvent vapor taken from an intermediate highlevel layer are condensed, and wherein undesirable constituentsareremoved from the system by contacting the vapor in said lake or in thecondensate formed therefrom with an inorganic adsorbent or combinationof adsorbents adapted to take up one or more of the undesirableconstituents present, including water, acids, and odoriferoussubstances; and it comprises apparatus adapted for application in thepractice of this process; all as more fully hereinafter set forth and asclaimed.

Vapor-phase degreasing systems are well known and widely employed forthe removal of grease, dirt, etc., from metal objects. In someinstances, sheet metal and other large objects are subjected to adegreasing treatment of this type, and in other instances nuts, boltsand other small machine elements are so treated, usually in baskets orracks adapted to hold a large number of these small pieces.

30 Any volatile grease solvent yielding heavy vapors, that is, ofcomparatively high molecular weight can be used, but in practicehalogenated derivatives of the aliphatic hydrocarbons are in generalfavor, and particularly trichlorethylene. All these halogenated bodieshave a tendency towards hydrolysis with development of acid in thepresence of moisture and in a body of hot vapor maintained in serviceover a period of time, the tendency may lead to annoying results.Moisture is constantly entering with the articles to be degreased.

Generally speaking, a vapor-phase degreaser consists of a reservoir forsolvent, means for heating and evaporating the solvent in the reservoir,a chamber for a body of evolved vapors above said reservoir, a coolingcoil or other cooling means at an appropriate height in said chamber toprevent the vapors from rising too far or passing into the air and outof the system, and means for conducting the articles to be degreased to,through and from the vapor chamber. This may include a suitable trolleysystem with baskets or racks for small parts to be treat-,

ier than the atmosphere in the chamber, they 10 Claims. (Cl. 202-46)tend to form a more or less uniform layer. At or near the desired uppersurface of this vapor layer or lake, cooling coils are provided on thesides of the chamber, and these coils are maintained at such temperaturethat any solvent vapors reaching them are condensed. The condensedvapors of clean solvent are ordinarily collected in an annular trough orchannel around the chamber below the cooling coils, and from this troughthe condensate is returned to the system. It is generally returned to aclean solvent reservoir separate from, but communicating with, theevaporator reservoir; and in some methods of operation, the articles tobe degreased are dipped in this clean solvent reservoir before passinginto the body of solvent vapors.

As stated, because of their relatively high specific gravity, thesolvent vapors tend to form a substantially uniform layer between theboiling solvent and the supernatant atmospheric layer.

In operation, there is, of course, an intermediate layer between thesolvent vapor and the normal atmosphere in which a certain amount ofsolvent vapor is mixed with air due to disturbances caused byintroducing articles to be degreased into the vapor lake and removingthem therefrom. Moisture entering the system tends to pass into thismixed layer as an azeotropic vapor mixture. This intermediate layergenerally does not extend substantially above the cooling coils,however, because the solvent content of such a layer, when propersolvents are employed, is readily condensed. When operating such asystem, it is generally desirable to so regulate the steam supply to theevaporating section that a minimum amount of solvent is condensed by thecooling coils. Condensation of very large amounts of solvent vaporinvolves a waste of both steam and cooling water. In order to maintain abody of solvent vapor of the desired depth, however, it is necessary tosupply a certain excess of heat units and to condense a certain amountof solvent.

When a vapor-phase degreasing system is operated, articles more or lesscoated with grease or commercially dry when it is introduced into thesystem, but under some climatic conditions, water is introduced into thesystem by condensation from the atmosphere, and also by the articlesdegreased. Water in the system is highly undesirable, however, bothbecause it disturbs the stratification heretofore described, and becauseit also tends to increase thev corrosion of metal equipment in contactwith the solvent and its vapors. Trichlorethylene is frequently employedas a solvent in vaporphase degreasing systems because water does notmake it very corrosive to metal, even at the boiling temperature.Cheaper solvents, such as carbon tetrachloride, for example, could beemployed to advantage, however,

if the water could be excluded from the system or promptly removedtherefrom before it has an opportunity to cause corrosion. The exclusionor removal of water is also advantageous in improving the effectivenessof the system and the uniformity of its operation with any solvent.

I have now found that the difficulties encountered because of theentrance of moisture into a vapor-phase degreasing system can be avoidedby providing in the system means for contacting the solvent vapors, orpart or all of the condensate formed therefrom, or both the vapors andthe condensate, with suitable inorganic adsorbents; and I have alsofound that by properly selecting these adsorbents, the acids which tendto form in the system even when using stabilized solvents can beeliminated. Still further, odoriferous substances formed from thegreases and other impurities collected in the system during operationcan also be eliminated by suitable adsorbent-s. The elimination of anyone of the undesired substances (water, acids and odoriferous bodies)from vapor-phase degreasing systems is an important advance in this art,and the simultaneous removal of two or more of these substances is ofgreat benefit from the standpoint of economy of operation, quality ofresults obtained, and convenience of operation.

For the removal of water or water-vapor from the system, I employ any ofseveral inorganic adsorbents of neutral or alkaline reaction. Forexample, I use such materials as silica gel, activated alumina andactivated bauxite, having an action in such systems which is essentiallyphysical; or I use calcined magnesia or activated magnesia or likematerials having a combined physical and chemical action. When removalof water is the sole desideratum, it is immaterial which of thesematerials is employed. However, even when employing the best stabilizersfor organic solvents which are now known, there is almost always someformation of acid during the operation of a degreasing system. It istherefore ordinarily desirable to employ an adsorbent having somechemical reactivity enabling it to remove the acids along with thewater. I therefore find it advantageous, as one specific embodiment ofmy invention, to employ an alkaline material such as some form ofcalcined magnesia, for the adsorbent in my process; but this alkalinematerial may be used, if desired, in admixture with a strictly physicaladsorbent such as silica gel.

As previously stated, during operation of a degreasing system thereaccumulate in the pool of boiling liquid varying quantities of oils,fats, gums, resins and miscellaneous organic substances removed from thearticles cleaned. Decomposition or oxidation of this organic matteroften results in the development of undesirable odors which, as is wellknown, are generally noticeable around any degreaser in service, andconstitute one of the unpleasant features of degreaser operation. Thisundesirable condition prevails even when the degreaser includescondensers so eflicient as to keep solvent loss quite low. Certainactivated adsorbents, such as the activated magnesia" made by carefuldehydration of hydrated magnesia, as disclosed and claimed in mycopending application Serial No. 26,006, filed June 11, 1935, have aselective adsorbing power for organic materials of the nature of theseodoriferous substances; and when activated magnesia or other suitableactivated adsorbents are. employed for the adsorption of water andacids, in accordance with another specific embodiment of my invention,there also results a substantially complete elimination of theheretofore objectionable odors from degreasing systems. It is clear, ofcourse that this deodorization can be effected without an accompanyingcomplete removal of water and acids, but it is generally desirable tosimultaneously effect removal of all of these undesirable elements fromthe system, and this constitutes an especially desirable embodiment ofmy invention.

After selection of an adsorbent or mixture of adsorbents adapted toaccomplish the desired purpose or purposes of any specific embodiment ofthe present invention, I apply the adsorbent material or mixture invarious ways. For example, a basket of perforated metal or wire screencontaining magnesium oxide or other adsorbent is suspended in the lakeor stratum of solvent vapor in the degreaser, and any vapor coming incontact with this adsorbent has undesired constituents removedtherefrom. I find that it is generally even more effective, however, toprovide a container of the selected adsorbent in the path of liquidcondensed solvent returning from the cooling coils to the degreaserreservoir. As previously stated, the usual vapor-phase degreaserincludes an annular channel or gutter which collects the condensedsolvent dropping from the cooling coils, and with such degreasers it isa simple matter to introduce a percolating tower containing magnesiumoxide or other selected adsorbent into the line returning the cleancondensed solvent from this collecting channel to the clean solvent wellor to any other desired part of the system. Part of the condensedsolvent may flow through this tower while part of it is by-passed aroundthe tower, directly back to the system, if desired.

In order that my invention may be more readily understood, it will nowbe described with reference to the accompanying drawing, in which thesingle figure is a more or less diagrammatic illustration of a crosssectional view of a vaporphase degreasing apparatus adapted foroperation in accordance with my invention, and constituting part of myinvention.

In the drawing, 2 indicates the walls or shell of a degreaser containinga bottom portion which is divided into a vaporizing section orevaporator 4 and a clean solvent well 6. The vaporizing section 4 isprovided with steam coils 8 which are supplied with steam from anysuitable source (not shown) in quantity suflicient to vaporize thedesired amount of solvent. The vaporized solvent rises into the chamberabove the vaporizing section to a predetermined level such as thatindicated by the line -9, and any substantial quantity of vapor risingabove this level is condensed by the cooling coils l2. These coils areadvantageously individually controlled, so that effective cooling can beaccomplished at any desired level. Condensate formed by the operation ofthe cooling coils I2 collects in the annular channel i l, from which itmay be returned to any desired part of the system, such as the cleansolvent well 6, through a pipe l6, for example.

This pi e ma be provided with an adjustable level regulator and a valveH3; or it may be omitted in which case condensed solvent overflows fromthe trough l4 into the well 6.

In one embodiment of my invention, a wire screen or perforated metalbasket 2|] containing granular calcined magnesium oxide or othersuitable adsorbent is suspended in the vapor stratum, and the adsorbenteffects the desired purification of the solvent vapor by removaltherefrom of water, acids and odoriferous substances, or some of theseundesired constituents.

In another and generally more advantageous embodiment of my invention,the condensate collected in the channel or gutter l4 passes through asuitable conduit 22, which may be equipped with a valve 23, into apercolating tower 24 or other suitable container. This container isadvantageously provided with a removable cap or cover 26, and aremovable basket of perforated metal or wire screen 28 fitting rathersnugly in its interior. This basket is filled with a suitable absorbentthrough which condensate delivered through the passage 22 must trickleor per'colate on its way back to the system. This results in aneffective purification of the condensed solvent, which then flowsthrough a pipe 30 back to the clean solvent reservoir 6. Part of thecondensed solvent may by-pass directly from the channel l4 back to theclean solvent reservoir through the pipe 16, if desired, with the valvel8 and the pipe I5 adjusted to maintain the desired level in the channelI4. Alternatively, the valve l8 may be closed entirely. If desired, Imay, of course, employ both the external percolating tower 24 and theinternal suspended basket 20, but it is seldom necessary or desirable toemploy both of these expedients simultaneously. Clean solvent collectedin the well 6 overflows into the evaporating section 4, where it isagain vaporized into the system; and I have found that in all theembodiments of my invention water, acids, and odoriferous substances arereadily eliminated or minimized when employing suitable adsorbents.

My invention has been described hereinabove with special reference tocertain types,of construction, methods of operation and choices ofadsorbents, which are now considered desirable, but it is to beunderstood that these references are by way of illustration only andthat the invention is not limited to them but may be variously embodiedand practiced within the scope of the appended claims.

What I claim is:

1. In a process of vapor-phase degreasing wherein a body of organicsolvent vapor of high molecular weight is established, and maintainedbetween an underlying boiling body of the liquid solvent and asupernatant atmospheric layer, with cooling and condensation of solventvapor passing upwardly above a predetermined level in said body of vaporand return of condensed solvent to the system, the improvementcomprising between an underlying boiling body of liquid solvent and asupernatant atmospheric layer, and wherein solvent vapor passingupwardly above a predetermined level in said body of vapor is condensedand returned to the system, the improvement comprising contactingvaporized solvent in said body of solvent vapor with an inorganicadsorbent to remove water therefrom.

3. In a process of vapor-phase degreasing, wherein a body of organicsolvent vapor of high molecular weight is established and maintainedbetween an underlying boiling body of liquid solvent and a supernatantatmospheric layer, and wherein solvent vapor passing upwardly above apredetermined level in said body of vapor is condensed and returned tothe system, the improvement comprising contacting liquid solventcondensed from said body of solvent vapor with an inorganic adsorbent toremove water from the solvent before it is returned to said body ofliquid solvent.

4. The method of claim 1, wherein at least a part of said inorganicadsorbent has an alkaline reaction and adsorbs acids from the vaporizedsolvent.

5. The method of claim 1, wherein said inorganic adsorbent comprises amixture of alkaline and non-alkaline adsorbent materials.

6. The method of claim 1, wherein at least a part of. said inorganicadsorbent is sufliciently activated to adsorb odoriferous organicimpurities from the vaporized solvent.

7. The method of claim 1,- wherein said inorganic adsorbent comprisesactivated magnesia.

8. Apparatus for vapor-phase degreasing, comprising a chamber forsolvent vapors, means communicating with said chamber from below forenclosing and boiling a body of liquid solvent, means for condensingsolvent vapor passing above a predetermined level in said chamber, meansfor returning solvent so condensed to the system, and means forcontacting solvent vaporized from said body of liquid solvent and beforeit is returned thereto with an enclosed mass of inorganic adsorbentadapted to remove water therefrom.

9. Apparatus for vapor-phase degreasing, comprising a chamber forsolvent vapors, means communicating with said chamber from below forestablishing and maintaining a boiling body of liquid solvent andfurnishing vapors to said chamber, means for condensing solvent vaporpassing above a predetermined level in said chamber,

10. Apparatus for vapor-phase degreasing comprising a chamber forsolvent vapors, means communicating with said chamber from below forestablishing and maintaining a boiling body of liquid solvent andfurnishing vapors to said chamber, means for condensing solvent vaporpassing above a predetermined level in said chamber, means for returningsolvent so condensed to the system, and means operatively connected withsaid means for returning condensed solvent to the system and adapted tocontact the condensed liquid solvent with an enclosed mass of inorganicadsorbent to remove water from the solvent.

MAX Y. SEA'I'ON.

